A commonly known process in which aryl alcohol is converted with the help of a catalyst is a process in which propylene oxide and styrene are produced starting from ethylbenzene. In general such process involves the steps of (i) reacting ethylbenzene with oxygen or air to form ethylbenzene hydroperoxide, (ii) reacting the ethylbenzene hydroperoxide thus obtained with propene in the presence of an epoxidation catalyst to yield propylene oxide and 1-phenyl ethanol, and (iii) converting the 1-phenyl ethanol into styrene by dehydration using a suitable dehydration catalyst.
A further well-known process comprises the manufacture of propylene oxide with the help of cumene. In this process, cumene is reacted with oxygen or air to form cumene hydroperoxide. Cumene hydroperoxide thus obtained is reacted with propene in the presence of an epoxidation catalyst to yield propylene oxide and 2-phenyl propanol. The latter can be converted into cumene with the help of a heterogeneous catalyst and hydrogen. Suitable processes are described for example in WO 02/48126.
It was found that in the preparation of aryl alcohol, by-products are formed. Such by-products can be dimers and trimers of the aryl alcohol such as bis(aryl alkyl)ethers. In the process in which ethylbenzene is used, a major part of the bis(aryl alkyl)ethers formed was found to consist of bis(α,α-phenyl ethyl)ether, which is assumed to result from the reaction between two molecules of 1-phenyl ethanol. These by-products such as dimers and trimers are difficult to separate from the aryl-alcohol while they can also be formed during separation. In the past, not a lot of attention was paid to the presence of these by-products in the aryl alcohol.
In the conventional process described in U.S. Pat. No. 3,351,635, the distillation of the aryl alcohol containing reaction mixture is described in general terms. In the examples, the bottom fraction of the distillation is dehydrated. The bottom fraction will contain substantial amounts of heavy by-products. In the process of GB-A-1,127,987, a substantial amount of relatively heavy compounds is formed at the conditions at which the distillation columns are operated. A substantial amount of these relatively heavy compounds is distilled overhead and is processed further together with the alpha phenyl ethanol or dimethyl benzyl alcohol. The process of U.S. Pat. No. 3,452,055 makes use of a vaporizer for separating the different compounds. Vaporizers tend not to separate aryl alcohol from the dimer and trimer by-products.